1. Technical Field
The present disclosure relates to a smart card, more particularly, to a smart card system configured to control the speed of an internal clock of the smart card to decrease power consumption and a corresponding method thereof.
2. Discussion of Related Art
A contactless smart card communicates with a smart card reader in accordance with the ISO 14443 protocol. The contactless smart card is designed to recover a command that the smart card reader transmits and to respond at the correct time.
In order to enable communications between the smart card and the smart card reader, which are separated by a great distance, the units must operate with a low power. As data output from the smart card reader is transferred in a wireless format, it is required that the circuits operate accurately. In other words, in order to respond within a predetermined period of time after a command from the smart card reader is received, the smart card may respond after counting with a clock having a high frequency, for example, 13.56 MHz. The high clock frequency (13.56 MHz), however, may be one of the causes of the high power consumption of the smart card.
As an example, a smart card that complies with the contactless Type A protocol transmits a request signal after a predetermined period of time upon receiving data from the smart card reader. In other words, in the case of data ending in ‘1’, the smart card transmits a response signal after a period of time (9*128+84)/fc (fc=13.56 MHz), and in the case of data ending in ‘0’, the smart card transmits a response signal after a period of time (9*128+20)/fc. In other words, the smart card counts using a counter operating at 13.56 MHz in order to transfer data after predetermined periods of time, either 1236/fc or 1172/fc. In this case, peak currents occur in the smart card at intervals of 13.56 MHz.